The Roman presence in the region can be described as having four phases from Augustus to Hadrian: military conquest under Augustus, and consequent military actions; the establishment of military bases along roads and river crossings under Claudius; the establishment of camps along the river for stationing legions and auxiliaries carried out by the Flavian dynasty and Trajan; and further expansion into Dacia north of the Danube. Hadrian's approach was to defend and maintain, a policy that remained more or less in effect until the latter 4th century, when Roman control dsintegrated.[6] The pattern of Roman settlement after the time of Hadrian became standard: a fort (castra), a military town (canabae) associated with it, and a town (municipium) developing two or three miles away.[7]

The Danubian population has been estimated as at least 2 million during the reign of Augustus, and 3 million in the 2nd century, but these figures are not based on hard data, and later archaeological investigations indicate a greater degree of development than had been recognized.[8] In the time of the Antonines, there were perhaps 3 to 6 million inhabitants.[9]